1. Field of the Invention
The present invention relates to a motor control device and an out-of-step detecting method of a stepping motor, and particularly, to a motor control device and an out-of-step detecting method of a stepping motor that measure a back electromotive voltage to detect out-of-step.
2. Description of the Related Art
A stepping motor has various features and is widely used. That is, the stepping motor has a long life due to its structure where there is no mechanical contact between stators and rotors. Also, large static torque is obtained when the stepping motor is in an excited state.
In the stepping motor, so-called out-of-step may occur, and occurrence of out-of-step may become a problem. If a stepping motor becomes out of step, a rotor cannot rotate normally. The out-of-step may occur, for example, when the period of a pulse signal is short or a load is large.
In general, the stepping motor is used for controlling the angle or speed of rotation at high accuracy. Since the stepping motor manages a rotation position according to the number of pulses from a control side, if detection of out-of-step is late and only control progresses, the position of a gear or the like, that is a driving object, may deviate. Also, if detection of out-of-step is late, sound noise may be caused. Therefore, in order to perform an appropriate operation in a device or the like using a stepping motor, it is required to quickly detect occurrence of out-of-step.
When a stepping motor is out of step, it is necessary to quickly detect the out-of-step and to perform error processing such as stopping rotation or returning to a normal rotation state. Therefore, in the stepping motor, a circuit or system for detecting out-of-step and then performing error processing is additionally used.
JP-A-2009-261045 discloses the following out-of-step detecting method. That is, only for a short time having no influence on rotation of a stepping motor, a control current of a coil of each phase of the stepping motor is halted by turns phase by phase. Then, when the control current is halted, a back electromotive voltage is measured, and if the measurement result satisfies a predetermined out-of-step detection criterion, occurrence of out-of-step is detected.
JP-A-2012-16221 discloses a control method of a motor configured to set all coils, other than a coil whose back electromotive voltage is measured when a control current is halted, to a fixed voltage, in addition to a method as disclosed in JP-A-2009-261045.
JP-A-2011-259525 discloses a motor control device that measures the back electromotive voltage of a motor during rotation, thereby detecting a state regarding out-of-step of a stepping motor.
JP-A-2000-166297 discloses a drive device of a stepping motor that stops output of a drive pulse such that energization of an excitation coil of the stepping motor is stopped, if an out-of-step detecting circuit detects occurrence of out-of-step. In this drive device, it is disclosed to detect occurrence of out-of-step based on a voltage variation caused by a back electromotive voltage.
JP-A-2005-039874 discloses a control device of a stepping motor configured to supply an excitation current to the stepping motor by a preheating control unit such that the stepping motor does not rotate, when a temperature measured by a temperature sensor for measuring an environmental temperature is lower than a predetermined threshold temperature.
JP-A-2006-014440 discloses a motor drive control device that detects a temperature state of a load mechanism such as a driving roller or a driven roller that a motor drives, and sets a drive current of the motor based on the detected temperature state.